Laser guidance system for grade control

ABSTRACT

A vehicular machine, such as a trencher, having working means, such as a digging wheel, carried thereon for working material to a desired grade as the machine moves along a given path. Vertical adjustment of the working means is automatically controlled by a laser guidance system mounted on the machine for movement therewith. The guidance apparatus includes a reference means, such as a shoe of a trencher, movable with the machine and which engages the surface of the material already worked to the desired grade by the machine. The guidance apparatus also includes a detector apparatus comprising a laser beam generator mounted on a stabilizing platform and a beam sensor remote therefrom but enclosed within the same housing, the housing being carried by the framwwork of the working implement of the machine. The stabilized laser is preferably located in close proximity to the reference means with the beam aimed generally in the plane of motion of the working implement relative to the machine. Deviations of the working means from the desired grade are sensed by relative motion between the beam and sensor to develop a control signal utilized by a hydraulically actuated hoisting mechanism to raise or lower the working means to thus correct for such deviations and thereby maintain the material being worked at the desired grade as the machine moves along said path.

United States Patent 1 Zimmer 1 Apr. 17, 1973 1 LASER GUIDANCE SYSTEM FOR GRADE CONTROL [76] Inventor: Walter George A. Zimmer, 11 Jeffrey Street, Chatham, Ontario,

Canada [22] Filed: Nov. 22, 1971 21 Appl. No.: 200,893

[52] US. Cl ..37/97, 33/185 V, 37/D1G. 20, 56/D1G. 15, 172/4.5, 299/1 [51 Int. Cl. ..E02f 5/08 [58] Field of Search 172/45, 4; 37/80, 37/97, DIG. 20; 299/1; 94/46 AC; 33/185 V; 56/DIG. 15

[56] 7 References Cited UNITED STATES PATENTS 3,604,512 9/1971 Carter et al ..l72/4.5 3,659,949 5/1972 Walsh et al. ..172/4.5 X 3,619,618 11/1971 Thorn et al. ..172/4.5 X 3,554,291 1/1971 Rogers et al.... ..l72/4.5 3,494,426 2/1970 Studebaker l ..172/4.5 3,641,351 2/1972 Hintringer et al. ...37/D1G. 20

Primary Examiner-Robert E. Pulfrey Assistant Examiner-Clifford D. Crowder Att0mey-Arthur Raisch et al.

[57] ABSTRACT A vehicular machine, such as a trencher, having working means, such as a digging wheel, carried thereon for working material to a desired grade as the machine moves along a given path. Vertical adjustment of the working means is automatically controlled by a laser guidance system mounted on the machine for movement therewith. The guidance apparatus includes a reference means, such as a shoe of a trencher, movable with the machine and which engages the surface of the material already worked to the desired grade by the machine. The guidance apparatus also includes a detector apparatus comprising a laser beam generator mounted on a stabilizing platform and a beam sensor remote therefrom but enclosed within the same housing, the housing being carried by the framwwork of the working implement of the machine. The stabilized laser is preferably located in close proximity to the reference means with the beam aimed generally in the plane of motion of the working implement relative to the machine. Deviations of the working means from the desired grade are sensed by relative motion between the beam and sensor to develop a control signal utilized by a hydraulically actuated hoisting mechanism to raise or lower the working means to thus correct for such deviations and thereby maintain the material being worked at the desired grade as the machine moves along said path.

28 Claims, 9 Drawing Figures PATENTEB APR 1 71973 SHEET 2 or 3 Y 55 88 52 96 92 4 67 56 55 I //3 I :1: m 97 l. '1 m... D... ,vJZ m? l! G) i 1;

W 1 :t: ;,,..'1 iii 30 X a h 2 4 4 0 I 78 9/ I LASER GUIDANCE SYSTEM FOR GRADE CONTROL This invention relates to machines for grading material in, on, or over terrain such as ditching, tunneling, grading and other similar-earth working machines, as well: as paving machines and the like, and more particularly to such machines with guidance systems for controlling the grade or elevation of the material graded by such machines.

Objects of this invention are to provide an improved machine for grading material, and an improved control system for sucha machine, which automatically controls and adjusts the grading implement of the machine during operation of the machine to maintain the material being worked by the machine at a desired predetermined grade.

Another object is to provide a machine and/or control system therefor of the above character which is self-contained and does not require any apparatus external to the machine and hence can be ready and quickly set up and adjusted, operates automatically after set up and adjustment, is rugged and durable, and produces within close tolerances the desired grade.

These and other objects, features and advantages of this invention will be apparent from the following description, appended claims and accompanying drawings in which:

FIG. 1 is a side elevational view of a ditching machine with a grade control including a detector apparatus embodying this invention mounted on the machine.

FIG. 2 is an enlarged side elevational view of the detector apparatus shown in FIG. 1.

FIG. 3 is a fragmentary isometric view of the detector apparatus with portions broken away to illustrate a laser light source and sensor units thereof.

FIGS. 4, 5 and 6 are side, end, and top views, respectively, partially in section of the laser light source unit of the detector apparatus.

FIG. 7 is a fragmentary side elevational view partially in section of a modified form of the detector apparatus.

FIG. 8 is a fragmentary vertical sectional view taken on line 8-8 of FIG. 7.

FIG. 9 is a schmatic diagram of the electric circuitry of the detector apparatus and the associated hydraulic system of the ditching machine.

Referring in more detail to the drawings, FIG. 1 illustrates a ditching machine 20 comprising a conventional six-wheel tractor vehicle 22 and a trenching unit 24 trencher unit 24 pivots in an upright plane about pivot point 41 at the trailing bottom edge of shoe 30. The forward end of frame 26 is raised and lowered by a conventional hydraulic ram and cable mechanism 42 fixed to tractor 22. The forward end of frame126 is pivotally connected to a saddle 44 slidably received on a pair of horizontally spaced and generally vertically extending rails or ways 46 rigidly fixed to the rear of the frame of tractor 22. Digging machine 20 including trencher unit 24 as thus far described is conventional and well known in the prior art and thus will notbe described in further detail.

The control system of machine 20 embodying this invention for automatically controlling the grade or elevation of bottom surface 38 of trench 34 has a detector apparatus 50 mounted on trencher unit 24. As shown in FIG. 2, detector apparatus 50 has a laser light source 52 mounted on a carrier plate 54 rigidly fixed through end plate 55 to one end of a long hollow tube 56. A sensor unit 58 is mounted in a closure 60 rigidly fixed to the other end of tube 56. A cabinet 62 with a control panel 64 ismounted exteriorly on tube 56. A removable cover'66 overlies carrier plate 54 and is releasably fastened thereto to enclose source 52. Source 52 comprises a conventional laser unit which generates a beam of highly coherent monochromatic light represented by broken line 68 which passes through tube '56 and impinges on sensor unit 58. Generally rectangular apertures 67 and 69 are provided in end plate 55 and sensor housing 60 respectively to allow light beam 68 to pass through tube 56 and strike sensor unit 58. Light beam 68 is slightly diffused by a suitable lens system 70 (FIG. 3) of source 52 so that beam 68 impinges on sensor unit 58 in a small, generally circular area or spot 72 rather than a single point. Source 52 can be a standard helium-neon gas laser driven from a l2-volt battery power source such as is commercially available from Nova Laser Systems, Inc. Ltd., 1825 Wyandotte St., Windsor, Ontario,

' Canada as Model Number Mark II and thus will not be towed by tractor 22. Trenching unit 24 has a rigid frame 26 with a digging wheel 28 mounted for rotation thereon about an axis 28' and a shoe 30 rigidly fixed thereto. Digging wheel 28 has a plurality of buckets or scoops 31 mounted thereon and is rotated via a chain drive 32 through a power take-off unit 33 of vehicle 22 to dig a trench 34 in terrain 36 as vehicle 22 moves over the terrain along the desired path of trench 34. The material removed by scoops 31 is dumped in a conveyor 35 which carries the material laterally away from digging wheel 28. Shoe 30 rides along the bottom surface 38 of trench 34 to iron out and smooth the bottom surface and is stabilized in the trench by a small fin 40 at its trailing edge. The grade or elevation of bottom surface 38 of trench 34 is varied and controlled by raising and lowering the front end of frame 26 so that described in further detail.

As shown in FIGS. 2 and 3, sensor unit 58 has two vertically stacked coplanar photovoltaic'solar cells 74 and 76 mounted in a frame 78 which is pivotally received in a yoke 80 for rotation on an axis generally transverse to light beam 68. Photocells 74 and 76 are electrically isolated from both frame 78 and each other and their adjacent ends are preferably spaced approximately 0.030 of an inch from each other. Yoke 80 is pivotally mounted on slide 82 by a bearing 84 for rotation on an axis generally parallel to light beam 68 and transverse to and intersecting the pivotal axis of sensor mounting frame 78. Slide 82 is mounted for reciprocation in a rectangular frame 86 fixed to an end wall of housing 60 and is reciprocated by a threaded shaft 88 extending through housing 60 with a manually operable crank handle 90 fixed to its exposed end (FIG. 2). A counter weight 91 fixed to the lower end of frame 78 provides a center of gravity for sensor unit 58 which is I 50 pitches up and down and as it rolls about its longitudinal axis.

As shown in FIGS. 3-6, source 52 is mounted on plate 54 by a gimbal 92 with a first generally rectangular, fourcsided carrier frame 94 and a second U-shaped carrier frame 96. Carrier frame 94 is mounted for rotation on a longitudinal axis generally parallel and generally coincident with light beam 68 by a pair of tubular front and rear coaxial hollow stub shafts 97 and 97' fixed to the front and rear walls respectively of frame 94. Shafts 97 and 97 are respectively journalled in bearin s 98 and 98 res ectivel received in vertig P Y cally extending supports 100' and 100 slidably connected for adjustment to track bars 102 and 102' fixed to support plate 54. A hole 104 in the front wall of frame 94 concentric with shafts 97 allows light beam 68 to pass through frame 94 via shaft 97 to impinge on sensor 58. Frame 96 of gimbal 92 is mounted in frame 94 for rotation on an axis perpendicular to the axis of rotation of frame 94 by a pair of opposed coaxial trunnions 106 each having a stub shaft 108 extending through the associated side wall of frame 94. Shafts 108 are received in coaxial bearing assemblies 110 mounted in opposed openings 112 in forks 113 of frame 96. Laser unit 52 is fixedly mounted to frame 96 for rotation therewith between spaced parallel mounting plates 115 fixed to forks 113 of frame 96. Laser light unit 52 is preferably mounted with the point from which light beam 68 eminates coincident with the point of intersection of the rotational axes of gimbal 92.

To retain laser light unit 52 in a stabilized attitude within predetermined limits, as detector apparatus 50 pitches and rolls, a pendulum 114 is fixed to the lower end of a rigid arm 116 which extends through a clearance hole 117 in carrier plate 54 and is fixed at its upper end to frame 96. Movement of pendulum 114 and thus movement of laser light unit 52'is dampened by a liquid 118, such as castor oil, received in a generally rectangular container 120 releasably secured and sealed to the lower face of carrier plate 54. The liquid 118 is prevented from escaping through clearance opening 117 by a flexible seal 122 received over arm 116 and secured and sealed to the lower face of carrier plate 54.

The rearward end of detector 50 is pivotally mounted on trencher unit 24 of ditching machine by a pair of opposed coaxial stub shafts 124 which are fixed to the side walls of cover housing 66 preferably coaxial with trunnions 106. As shown in FIG. 1, shafts 124 are pivotally received in the upper ends of a pair of horizontally spaced arms 126 of a support bracket 127 fixed to the rear of frame 26. The forward end of detector 50 is supported by a threaded shaft 128 which is connected to tube 50 adjacent its forward end and secured by jam nuts 130 to a bracket 132 fixed to frame 26. Detector apparatus 50 is thus adjustably mounted on trencher unit 24 with its longitudinal axis extending generally parallel to the longitudinal dimension of trench 34 produced by the trenching unit. The entire detector, including sensor 60, can be pivoted about the axis of shafts 124 by adjusting nuts 130 on shaft 128 to thereby facilitate initial set up wherein tube 50 is oriented with the longitudinal axis preferably generally parallel to the desired grade of the bottom surface 38 of the trench. Preferably, detector 50 is also mounted so that lateral gimbal axis of light beam 68 is generally vertically above point 41 about which trencher unit 24 pivots as indicated by vertical center line 134 in FIG. 1.

The foregoing mounting of detector 50 is intended to accommodate use of ditching machine 20 on terrain 36 which is inclined at not more than about say a 2 or 3% grade. If more steeply inclined terrain is encountered, arm 116 of pendulum 114 will strike the edge of hole 117 in carrier plate 54 and prevent laser 52 from assuming a stabilized attitude. Accordingly, to allow laser 52 to assume a stabilized attitude when digging machine 20 is used on more steeply inclined terrain, the angular relationship between pendulum 114 and laser unit 52 is made adjustable by a modified mounting structure shown in FIGS. 7 and 8. In this modified form, laser 52 is fixed as by welds 136 to a steel plate 138 pivotally mounted on frame 96 of gimbal 92 at a point coincident with the axis of rotation of frame 96. Mounting plate 138 is releasably secured in various angular positions in relation to pendulum 114 by a threaded bolt 140 engaging a guide plate 142 fixed to carrier frame 96. Bolt 140 extends through an arcuate slot 144 in plate 142 and a graduated scale 146 adjacent the slot indicates the angular position of laser 52 relative to pendulum 114.

Detector 50 has electric control circuitry 150 schematically illustrated in FIG. 9 which is mounted in control panel 62. In response to the position of light beam 68 on photocells 74 and 76, electric circuitry 150 operates and controls a conventional electro-hydraulic, four-way directional control valve 152 connected to a source of pressure fluid for controlling supply of such fluid to a hydraulically actuated cylinder 154 of hoist mechanism 42 for raising and lowering trenching unit 24. Electric relays l-CR and 2-CR mounted in panel 62 control the supply of current from a source 156 to a force motor 158 of hydraulic valve 152 which actuates a pilot spool which in turn controls the main spool of the valve. Current source 156 may comprise two 12- volt batteries 160 and 162 with one terminal of each battery, 164 and 166 respectively, of opposite polarity connected to ground. The other opposite polarity terminals of batteries 160 and 162 are connected across one end of a pair of leads 168 and 170. Normally open contacts 1-C1 and 2-Cl of control relays l-CR and 2- CR respectively are connected in series with leads 168 and 170 respectively, and the other ends of leads 168 and 170 are connected to one terminal 159 of force motor 158, the other terminal of which is connected to the ground. The output terminals 188 and 188' of operational amplifiers 182 and 184 are respectively connected through normally closed contacts 2-C2 and l-C2 to one side of the coils of relays I-CR and 2-CR, the other terminal of the coils being grounded. Potentiometers 198 and 198 are connected in parallel across leads 168 and 170 to provide individual adjustment of the point at which each operational amplifier 182 and 184 saturates. A slide 200 and 200' of each potentiometer 198 and 198' is connected to input terminal and 180 of its associated operational amplifier 182 and 184 through a lead 202 and 202' and a resistor 204 and 204' which limits the input current from the potentiometer to its associated operational amplifier. Operational amplifiers 182 and 184 are protected from an overload at output terminals 188 and 188' by limiting resistors 206 and 206 connected across output terminals 188 and 188 and input terminals 180 and 180 through leads 202 and 202'. Electric power for operational amplifiers 182 and 184 is provided by leads not shown in FIG. 9 through a master power switch 207 mounted on control panel 64 (FIG. 2). A center zero galvanometer 208 for nulling the output of the photocells 74 and 76 during adjustment of apparatus 50 as explained hereinafter is connected in series with a switch 209and terminals 178 of photocells 74 and 76. Null meter 207 and switch 208 are mounted on control panel 64. Potentiometers 198 and 198 are mounted on control panel 64 and can be manually adjusted by turning knobs 210 and 210 respectively connected thereto.

Photocells 74 and 76 are of the photovoltaic type which generate an output current proportional to the amount of light striking the cell. Such cells are commercially available as catalog No. IN 240 CG from Centralab,'Inc., Semi-Conductor Division of Globe- Union, Inc. of El Monte, Calif. Suitable operational amplifiers 182 and 184 are commercially available as model No. LM-20l from National Semi-Conductor Corp., San Ysidro Way, Santa Clara, Calif. 95051. A model LM-20l operational amplifier has two input channels, one of which is grounded as shown in the schematic of FIG. 9. With these particular commercially available photovoltaic cells and operational amplifiers suitable values for resistors 186-186, 198-198 204-204, and 206-206 respectively are 10K, 50K, 100K and 1 Meg. ohms, respectively.

As illustrated schematically in FIG. 9, ditching machine has a hydraulic system with a reservoir 21 1 connected to the outlet of hydraulic valve 152 and the inlet of a pump 212 the discharge or high pressure side of which is connected to the inlet port of valve-152. The control ports 214 and 216 (conventionally designated ports A and B) of hydraulic valve 152 are connected by suitable conduits 218 to the opposed ends of hydraulic cylinder 154. A suitable hydraulic control valve 152 is commercially available as Model PVE-IOOO from SL1 Industries, 14740 Arminta St., Van Nuys, Calif. 91402. This model is a proportional pilot-operated four-way directional control valve actuated by aforce, motor which can be energized by a 12- volt DC power source. Electric circuitry 150 does not utilize the proportional control feature of this valve which has been selected because of its rapid response to the switching of its force motor by the control relays rather than for its proportional control feature per se.

To use detector apparatus 50, it is mounted on ditching machine 20 (as shown in FIG. 1) with one end.

adapted to move generally vertically with digging wheel 28 and the other end adapted to pivot about a point which is in a fixed relationship with a reference point i (such as point 41) on the bottom surface 38 of trench 34 with the reference point moving with the digging machine as wheel 28 produces the bottom surface of the trench. Preferably, detector apparatus 50 is mounted so that it pivots about the common point of intersection of the transverse axes of rotation of gimbal 92 which is preferably coincident with the point of emination of light beam 68. This pivot point preferably is on a generally vertical line (such as line 134) extending through the reference point which preferably is point 41 about which trenching unit 24 pivots or rocks to control the grade or elevation of bottom surface 38 of the trench.

In setting up and adjusting detector apparatus 50 to control the grade of the bottom surface 38 of trench 34, digging machine 20 is initially operated in a conventional manner by manually manipulating the conventional control levers (not shown) to raise and/or lower digging wheel 28 through cable and hydraulic mechanism 42 to bring the shoe 30 and point 41 to the desired grade of bottom surface 38 in an initial portion of the trench. Laser unit 52 and control circuitry are energized by turning on switch 207. With trenching unit 24 in the initial portion of trench 34, produced by manually'controlling the machine and with shoe 40 resting on this initial portion of surface 38 at the desired grade, sensor unit 58 is shifted generally vertically so that laser beam 68 is centered between and impinges equally on both photocells 74 and 76. Sensor unit 58 is adjusted to center beam 68 by manually adjusting threaded screw 128 to pivotally move detector apparatus 50 so that beam 68 is approximately centered and the beam is precisely centered by adjusting threaded screw 88 to raise or lower sensor unit 58 relative to tube 52 of the detector apparatus. Null meter 208 is connected across photocells 74 and 76 by turning on or closing switch 209 to provide an indicator for determining when beam 68 is centered between the photocells so that they have equal outputs. After beam 68 is centered, switch 209 is turned off to deactivate null meter 208. In some situations such as where the pitch or slope of the terrain is very steep, the modified form of detector apparatus of FIGS. 7 and 8 is used so that laser unit 52 will be free to swing in gimbal 92. In this modified form the angular relationship of pendulum 114 to the laser unit is also adjusted in rough centering beam 68 between photocells 74 and 76.

After beam 68 has been centered, tractor 22 is driven by the operator over terrain 36 along the desired longitudinal path of trench 34 and detector 50 automatically controls the raising and lowering of digging wheel 28 to produce-the desired grade of bottom surface 38. If, for example, tractor 22 goes over a high spot in terrain 36, digging whee128 will be raised above the desired elevation of surface 38- and, hence, detector apparatus 50 will energize cable and hydraulic mechanism 42 to lower digging wheel 28 and when the tractor goes over a low spot in the terrain 36, wheel 28 will be urged below the desired elevation of surface 38 and detector apparatus 50 will energize mechanism 42 to raise digging wheel 28 to the desired elevation. Whenever light beam 68 is deflected from its center position between photocells 74 and 76, circuitry 150 in conjunction with hydraulic directional valve 152 and hydraulic cylinder 154 of mechanism 42 operates as a servomechanism to raise or lower digging wheel 28 so that light beam 68 is again centered between the" photocells. For example, when a high spot in terrain 36 shifts tractor 22 so that digging wheel 28 is raised above the desired elevation, detector 50 is pivoted upwardly with the frame 26 about the pivot point 41 while laser light source 52 remains in a stabilized attitude due to gimbal 94 and pendulum 114 so that more light of beam 68 impinges on photocell 76 which increases the magnitude of its positive output current. When the magnitude of this positive output current exceeds the negative bias current at input terminal set by potentiometer 198, operational amplifier 184 saturates and produces an outputcurrent at terminal 188 which energizes the coil of control relay 2-CR. Energizing control relay 2-CR closes normally open contacts 2- C1 which causes current from source 156 to flow in one direction through force motor 158 and shifts the pilot spool of hydraulic valve 152 in one direction from its neutral position, thereby admitting hydraulic fluid under pressure through outlet port 214 into the rod end of hydraulic cylinder 154 to retract its rod and thereby extend the cable of mechanism 42 to lower digging wheel 28 to the desired elevation and return light beam 68 to its center position between the photocells. Similarly, when a low spot in terrain 36 shifts tractor 22 so that digging wheel 28 is lowered below the desired elevation, detector 50 is pivoted downwardly with frame 26 about point 41 while laser light source 52 remains in a stabilized attitude so that more light of beam 68 impinges on photocell 74 which increases the magnitude of its positive output current. When the magnitude of this positive output current exceeds the negative bias current at input terminal 180, set by potentiometer 198, operational amplifier 184 saturates and produces an output current at terminal 188 which energizes the coil of control relay l-CR. Energizing control relay l-CR closes normally open contact l-Cl and thus causes current to flow in the opposite direction through force motor 158, thus shifts the pilot spool of hydraulic valve 152 in the opposite direction from its neutral position, thereby directing hydraulic fluid under pressure through port 216 into the head end of cylinder 154 to extend its rod and thereby shorten the cable of mechanism 42 to raise digging wheel 128 to the desired elevation and return light beam 68 to its center position between the photocells. By adjusting potentiometers 198 and 198, the magnitude of the bias on inputs 180 and 180' of operational amplifiers 182 and 184 can be varied and, hence, the extent to which beam 68 can deviate or be displaced from the center position between photocells 74 and 76 before the servo action is initiated to return the beam to the center position can be adjusted and controlled. Thus, the extent of the deviation of digging wheel 28 from the desired elevation of bottom surface 38 of trench 34, can be adjusted and controlled. Each relay l-CR and 2-CR has a normally closed contact 2-C2 and 1-C2 respectively in the circuit for energizing the coil of the other relay so that both relays cannot become simultaneously energized which would provide a short across power source 156 through force motor 158 of hydraulic valve 152.

Both laser light unit 52 and photocell sensor unit 58 are gimbaled and weighted with pendulums to provide a center of gravity below the intersection of the transverse axes of the gimbals so that the units will remain in stabilized attitudes as the ditching machine pitches and rolls. Thus, only the generally vertical displacement of digging wheel 28 relative to reference point 41 as it moves along the bottom surface produced by digging wheel 28 is indicated by the deflection of beam 68 from its center position between photocells 74 and 76. In one working embodiment, a detector device comprising the aforementioned laser light unit Model No. Mark II of Nova Laser Systems, Inc., and photovoltaic sensor cells Model IN 240 CG of Centralab Inc., with a longitudinal spacing of ten feet between the photocells and the point from which the light beam eminates from the laser light source, was mounted as shown in FIG. 1 on a tandem wheel traction farm trencher manufactured by Zimmer Brothers Farm Drainage Ltd. of Chatham, Ontario. This trencher is similar to but more rugged than like trenchers made by Speicher Brothers, Inc., 308 Portland St., Celina, Ohio, and is adapted to dig up to 6 foot deep trenches. On such a unit, detector 50 operates satisfactorily and has produced a trench 34 with a bottom surface 38 which was within plus or minus one-eighth of an inch of the desired grade orelevation in a lineal length of the trench of feet. In operation, the mechanical vibration of the trencher causes the gimbals or rotary mountings of the laser light and photocell sensor units to oscillate about their stabilized positions rather than come to rest in these positions, which is believed to improve the accuracy and response time of the detector apparatus. Similarly, the hydraulic and mechanical system for raising and lowering the digging wheel to control the elevation of the bottom surface of the trench tends to slightly overshoot and hunt for the desired elevation so that it oscillates about the position producing the desired elevation rather than coming to rest at such position, which further improves the accuracy and response time of the trencher. Where the terrain is reasonably flat or the trencher is stabilized so that it does not roll or tilt sideways significantly as it moves across the terrain, mounting the sensor unit 58 in an adjustable fixed position so that it is not free to pivot, and monnting the laser light unit so that it is free to rotate on only one axis generally horizontal and transverse to the travel of the trencher and hence is stabilized with respect to only the pitching of the trencher, has worked satisfactorily.

From the foregoing description, it will now be apparent that the present invention provides an improved apparatus for guiding or controlling a vertically adjustable working implement as the same operates to maintain a desired grade of the material being worked by the implement along the path of travel of the machine carrying or propelling the implement. By mounting the entire detector apparatus 50 on machine 20 which carries or propels the working implement 28, there is no need to provide or establish remote sighting stations or associated equipment, thereby eliminating a substantial cost item not only in equipment but also in set-up labor. Moreover, the self-contained nature of the detector and guidance system of the present invention enables the machine to be used under extremely adverse field conditions due to the laser beam being completely protected by tube 56 from the surrounding environment. Also due to the fact that the beam 68 need not traverse open air between a remote station and machine 20, it is not affected by dust, haze or contaminated atmosphere and cannot be obstructed by intervening obstacles along the path of working such as trees, brush, changes in terrain or the like. The detector apparatus 50 and associated control equipment as disclosed previously herein has also proven to be extremely rugged since it has been found capable of withstanding the extreme shocks and vibrations normally en countered on a trenching machine of the character described.

In prior existing laser beam vehicle guidance systems using a source of laser light mounted stationarily and remote from the entire machine and a sensor mounted on the machine, side tilt of the machine will change the elevation of the sensor because it travels through an arc during tilting motion of the 'machine. This in turn will produce a false reading of a change in elevation where in fact the working implement such as the digging wheel or the tractor towing the digging wheel has not changed its elevation. However, with the present invention both the stabilized source 52 of the laser beam as well as the remote sensor 58 are preferably attached to an essentially rigid framework 26 or to other similar portions of an equivalent machine. Therefore, the beam source and sensor change elevation together during side tilt or sway of the machine as it moves along the grade being worked, and hence this motion does not introduce error into the guidance system.

' It is to be understood that in the case of a'trencher, road grader or other similar construction equipment having a fore and aft relationship between the vehicle and working implement, tube 56 is oriented so as to extend in the direction of travel of the machine along the path of material being worked. As used in this description and appended claims, this means that tube 56 and hence beam 68 will extend generally parallel to the direction of travel, it being understood that detector 50 can be oriented with sensor 60 mounted either ahead of or behind source 52 relative to the forward movement of the machine. However, it is also contemplated that the detector 50 of the present invention may be used to control theelevation of a working implement mounted to extend laterally of a construction machine in applications where the relative motion between the working implement and the machine which is carrying the same occurs on a plane which is perpendicular or otherwise laterally or transverse to the direction of forward travel of the machine. When controlling an implement of this character, detector 50 is mounted such that tube 56 extends generally parallel to the plane of such relative motion. One end of the framework of detector 50, such as sensor 60, is rigidly supported on the adjustable working implement for movement therewith and the other end, such as housing 66, is supported, as by a pivotal mounting previously described herein, on a suitable reference platform of the machine so that it is maintained in a predetermined relationship with a portion of the machine which senses or rides on the material which has already been worked to the desired grade.

It is also to be understood that it is preferred to mount detector 50 as closely as possible to the portion of the machine, such as shoe 30, which is sensing the grade of the material already worked. For example, in the case of the automatically guided trencher described previously herein detector 50 is mounted with source 52 on the vertical center line 154 which extends through the pivot point 4] of the shoe 30. Because the digging wheel frame 26 may be lowered relative to the tractor 22 an amount sufficient to dig a trench of up to say 6 feet in depth, detector 50 is mounted high enough on frame 26 to remain above and clear of even the deepest trenches being dug. However, inapplications such as road grading or the like where the working implement is operating essentially at or slightly above the surface level of the surrounding terrain, it is preferred to mount detector 50 within a foot or less of the portion of the machine which is riding on or otherwise sensing the grade of the material which has already been worked to the desired grade by the machine.

It will be noted that sensor 58 is preferably mounted on machine 20 at a point remote from the machinemounted source 52, say 10 to 30 feet. Such spacing provides an amplification of the travel of the beam spot 72 impinging on photocells 74,76: i.e., only a slight relative movement between the stabilized source 52 and its supporting framework as frame 26 pitches up and down will cause a relatively large amount of relative travel between the beam spot and the photocells. Hence, sensor 58 is capable of detecting very slight changes in elevation of the forward] end of the frame 26 while still employing a relatively simple and rugged sta bilizing apparatus in the form of the pendulum weight 114. This characteristic also makes it possible to construct detector 50 as a very rugged and strong piece of equipment which is capable of withstanding the very severe shocks and vibrations produced by a trenching machine or the like during normal operation thereof.

lclaim:

l. A machine for working material to a desiredgrade along a given path in, on or over terrain comprising a vehicle for moving upon said grade, working means carried by said vehicle for working the material to the desired grade as the vehicle moves on the terrain along the given path, said working means being vertically adjustable relative tosaid vehicle, reference means movable with the machine and adapted to engage with the surface of the material worked on by said working means at a location wherein the surface of the material has been worked to substantially the desired grade by said working means, generator means for producing a beam of radiant energy in the general direction of travel of said working means, sensor means spaced from said generator means and adapted to sense said beam of radiant energy, first carrier means carrying one of said generator means and said sensor means in a given relationship with said reference means for generally vertical movement therewith, second carrier means carrying the other of said generator means and said sensor means in a given relationship with said working means for generally vertical movement therewith, stabilizing means for maintaining the beam of radiant energy produced by said generator means in a given stabilized attitude to project in a plane generally parallel to the path of travel of said working means, said sensor means being disposed generally transversely to and intersecting said beam of radiant energy, said sensor means detecting relative motion between said sensor means and the point at which said beam of radiant energy strikes said sensor means caused by relative .genlrally vertical movement between said reference means and said working means and generating a signal indicative of vertical deviation of said working means from the desired grade, and control means responsive to said signal to adjust said working means generally vertically to correct for said deviation such that the material being worked remains at the desired grade as said working means is moved by said axis of rotation extending generally horizontally and transversely to said first axis of rotation, said generator means being carried by said gimbal, and a pendulum weight rigidly connected with said generator means for pivotal movement therewith on said second axis of said gimbal with the combined center of gravity of said generator means and said pendulum weight being generally vertically below said second axis of said gimbal.

4. The machine of claim 3 wherein the point of intersection of said first and second axes of said gimbal is generally on a vertical center line from the point at which said reference means engages the material worked on by said working means.

5. The machine of claim 3 which also comprises means connecting said pendulum weight with said second carrier such that the angular relationship between said second carrier and said pendulum weight can be adjusted.

6. The machine of claim 1 wherein said sensor means is mounted for rotational movement in a plane generally transverse to said beam of radiant energy on an axis generally parallel thereto.

7. The machine of claim 1 wherein said sensor means is mounted to pivot on a generally horizontal axis generally transverse to said beam of radiant energy and the center of gravity of said sensor means is generally vertically below said generally horizontal rotational axis.

8. The machine of claim 1 wherein said generator means is in a given relationship with said reference means for movement therewith and said sensor means is in a given relationship with said working means for movement therewith.

9. The machine of claim 1 wherein said working means comprises a digging wheel having a plurality of circumferentially spaced buckets thereon adapted to produce when rotated, a trench having a bottom surface in the terrain, and said reference means comprises a shoe adapted to be received in said trench behind said diggingwheel and to bear on said bottom surface of said trench.

10. The machine of claim 9 which also comprises an enclosure having a rigid hollow tube, a sensor housing connected to said tube adjacent one end thereof, and a generator housing connected to said tube adjacent the other end thereof with said sensor means mounted in said sensor housing and said generator means mounted in said generator housing such that said beam of radiant energy produced by said generator means passes through said hollow tube and impinges on said sensor means.

11. The machine of claim 10 in which said first carrier means comprises means pivotally mounting said generator housing on said shoe and said second carrier means comprises generally vertically adjustable means mounting said enclosure adjacent said one end of said tube in an adjustable given relationship to the axis of rotation of said digging wheel.

12. The machine of claim 1 wherein said working means comprises a rigid frame pivotally connected adjacent one end-thereof to said vehicle and a digging wheel mounted on said frame for rotation thereon and having a plurality of circumferentially spaced buckets adapted to dig a trench having a bottom surface when said wheel is rotated in the terrain, and said reference means comprising a shoe positioned behind said digging wheel and fixed to said frame, said shoe being adapted to be received in the trench produced by said digging wheel and to bear on the bottom surface of said trench with said shoe, frame and digging wheel being adapted to be pivoted in the trench about a point adjacent the trailing lower edge of said shoe as said one end of said frame is raised and lowered to control the grade of the bottom surface of the trench produced by the digging wheel, said generator means being carried by said first carrier means so that the point from which said beam of radiant energy eminates from said generator means lies generally vertically over said pivot point adjacent the lower trailing edge of said shoe.

13. The machine of claim 1 which also comprises a detector apparatus enclosure having a rigid hollow tube, a sensor housing connected to said tube adjacent one end thereof, and a generator housing connected to said tube adjacent the other end thereof with said sen sor means mounted in said sensor housing and said generator means mounted in said generator housing such that said beam of radiant energy produced by said generator means passes through said hollow tube and impinges on said sensor means.

14. The machine of claim 13 which also comprises means mounting said sensor means in said sensor housing for adjustment of said sensor means generally transversely to said beam of radiantenergy comprising a slide, an adjustment screw operably connected with said slide and being adapted to be manually rotated externally of said sensor housing to generally vertically reciprocate said slide within said sensor housing, and gimbal means carried-by said slide with said sensor means mounted on said gimbal means.

15. The machine of claim 1 wherein said sensor means comprises at least two photocellsproducing said electric signal indicative of vertical deviation of said working means from the desired grade, and said control means responsive to said electric signal comprises a hydraulic cylinder with a ram therein operably connected with said working means for vertically adjusting the position of said working means relative to said vehicle, an electro-hydraulic control valve adapted for selectively directing a hydraulic fluid under pressure into said cylinder to move said ram in said cylinder, and electric circuitry utilizing said electric signal of said sensor means to actuate and control said electrohydraulic valve to direct hydraulic fluid under pressure into said cylinder to move said ram to adjust said working means to correct for said deviation of said working means from the desired grade as said working means is moved by said vehicle along the path of travel of the grade.

16 A guidance system for controlling a working means carried by a machine for working a material to a desired grade as the machine travels along a given path by adjusting the working means relative to the machine, and sail40 machine having a reference means movable with the machine and adapted to engage with the surface of the material previously worked to the desired grade by said working means, said guidance system comprising generator means for producing a beam of radiant energy generally in the direction of travel of the working means, stabilizing means for maintaining the beam of radiant energy produced by said generating means in a given stabilized attitude to project in said direction of travel of the working means, said stabilizing means being adapted for mounting in a given relationship with one of said working meand and said reference means, sensor means extending generally transverse to and intersecting the beam of radiant energy produced by said generating means, said sensor means being spaced from said generating means and adapted for mounting in a given relationship with the other one of said working means and said reference means, said sensor means detecting relative motion between said sensor means and the point at which the beam of radiant energy impinges on said sensor means caused by relative movement between said referance means and said working means to produce an electric control signal indicative of deviation of said working means from the desired grade, whereby said electric control signal can be utilized to adjust said working means relative to the machine such that the material is worked to the desired grade as the working means is moved by the machine.

17. The guidance system of claim 16 wherein said generator means comprises a laser light source.

18. The guidance system of claim 17 wherein said stabilizing means comprises a gimbal having a first carrieradapted for rotation on an axis generally parallel to the beam of radiant energy produced by said laser light source and a second carrier mounted for rotation on said first carrier on an axis generally transverse to said axis of rotation of said first carrier, said laser light source being mounted on said second carrier for rotation therewith with the point from which the beam of radiant energy eminates generally coincident with the point of intersection of the axes of rotation of said first and second carriers, and a pendulum weight fixed to said second carrier such that the center of gravity of the combined laser light source, second carrier and pendulurn weight is generally vertically below the point of intersection of the axis of said first and second carriers.

19. The guidance system of claim 18 which alsocomprises 'a container receiving said pendulum weight therein and adapted to retain a liquid therein whereby the pivotal movement of said pendulum about the axes of said first and second carriers is dampened by the liquid.

20. The guidance system of claim 18 which also comprises means connecting said pendulum wieght with said second carrier such that the angular relationship between said second carrier and said pendulum weight can be adjusted.

21. .The guidance system of claim 17 wherein said sensor means comprises at least one photovoltaic cell.

7 22. The guidance system of claim 16 which also comprises means mounting said sensor means so that said sensor means can rotate on an axis generally parallel to the beam of radiant energy produced by said generator means.

23. The guidance system ofclaim 16 which also comprises means mounting said sensor means so that it can rotate on a first axis generally parallel to the beam of radiant energy produced by said generator means and can also rotate on a second axis generally transverse to the beam of radiant energy produced by said generator means and in which the center of gravity of said sensor means is generally vertically below the point of intersection of said first and second axes of rotation of said means for mounting said sensor means. i

24. The guidancesystem of claim 17 which also comprises an enclosure having a rigid hollow tube, a sensor housing connected to said tube adjacent one end thereof, and a generator housing connected to said tube adjacent the other end thereof, with said sensor means mounted in said sensor housing and said generator means mounted in said generator housing such that said beam of radiant energy produced by said generator means passes through said hollow tube and impinges on said sensor means.

25. The guidance system of claim 16 wherein said sensor means comprises at least two photocells producing said electrical control signal indicative of vertical deviation of said working means from the desired grade and the guidance system also comprises electric circuitry utilizing said electric control signal of said sensor means to actuate and control an electro-hydraulic valve of the machine to direct hydraulic fluid under pressure into a fluid motor of the machine to adjust the working means to correct for said deviation of said working means from the desired grade as the machine travels along a given path such that the material is worked to the desired grade.

26. A machine for working material to a desired grade along a given path in, on or over terrain comprising a vehicle for moving upon said grade, working means carried by said vehicle for working the material to the desired grade as the vehicle moves on the terrain along the given path, said working means being vertically adjustable in a given plane of motion relative to said vehicle, reference means movable with the machine and adapted to engage with the surface of the material worked on by said working means at a location .wherein the surface of the material hasbeen worked to substantially the desired grade by said working means, generator means for producing a beam of radiant energy in the general direction of said motion plane, sensor means spaced from said generator means and adapted to sense said beam of radiant energy, first carrier means carrying one of said generator means and said sensor means in a given relationship with said reference means for generally vertical movement therewith, second carrier means carrying the other of said generator means and said sensor means in a given relationship with said working means for generally vertical movement therewith, stabilizing means for maintaining the beam of radiant energy produced by said generator means in a given stabilized attitude to project in said motion plane, said sensor means being disposed generally transversely to and intersecting said beam of radiant energy, said sensor means detecting relative motion between said sensor means and the point at which said beam of radiant energy strikes said sensor means caused by relative generally vertical movement between said reference means and said working means and generating a signal indicative of vertical deviation of said working means from the desired grade, and control means responsive to said signal to adjust said working means generally vertically to correct for said deviation such that the material being worked remains at the desired grade as said working 'means is moved by said vehicle along said given path.

27. The machine of claim 26 wherein said generator means Comprises a laser light source.

28. The machine of claim 27 wherein said stabilizing means comprises pivot means having an axis of rotation by said pivot means, and a pendulum weight rigidly connected with said generator means for pivotal movement therewith on said axis with the combined center of gravity of said generator means and said pendulum extending generally horizontally and transversely to weight being generally Vertically below Said i said motion plane, said generator means being carried 

1. A machine for working material to a desired grade along a given path in, on or over terrain comprising a vehicle for moving upon said grade, working means carried by said vehicle for working the material to the desired grade as the vehicle moves on the terrain along the given path, said working means being vertically adjustable relative to said vehicle, reference means movable with the machine and adapted to engage with the surface of the material worked on by said working means at a location wherein the surface of the material has been worked to substantially the desired grade by said working means, generator means for producing a beam of radiant energy in the general direction of travel of said working means, sensor means spaced from said generator means and adapted to sense said beam of radiant energy, first carrier means carrying one of said generator means and said sensor means in a given relationship with said reference means for generally vertical movement therewith, second carrier means carrying the other of said generator means and said sensor means in a given relationship with said working means for generally vertical movement therewith, stabilizing means for maintaining the beam of radiant energy produced by said generator means in a given stabilized attitude to project in a plane generally parallel to the path of travel of said working means, said sensor means being disposed generally transversely to and intersecting said beam of radiant energy, said sensor means detecting relative motion between said sensor means and the point at which said beam of radiant energy strikes said sensor means caused by relative generally vertical movement between said reference means and said working means and generating a siGnal indicative of vertical deviation of said working means from the desired grade, and control means responsive to said signal to adjust said working means generally vertically to correct for said deviation such that the material being worked remains at the desired grade as said working means is moved by said vehicle along the path of travel of the grade.
 2. The machine of claim 1 wherein said generator means comprises a laser light source.
 3. The machine of claim 1 wherein said stabilizing means comprises a gimbal having a first axis of rotation extending generally parallel to the beam of radiant energy produced by said generator means and a second axis of rotation extending generally horizontally and transversely to said first axis of rotation, said generator means being carried by said gimbal, and a pendulum weight rigidly connected with said generator means for pivotal movement therewith on said second axis of said gimbal with the combined center of gravity of said generator means and said pendulum weight being generally vertically below said second axis of said gimbal.
 4. The machine of claim 3 wherein the point of intersection of said first and second axes of said gimbal is generally on a vertical center line from the point at which said reference means engages the material worked on by said working means.
 5. The machine of claim 3 which also comprises means connecting said pendulum weight with said second carrier such that the angular relationship between said second carrier and said pendulum weight can be adjusted.
 6. The machine of claim 1 wherein said sensor means is mounted for rotational movement in a plane generally transverse to said beam of radiant energy on an axis generally parallel thereto.
 7. The machine of claim 1 wherein said sensor means is mounted to pivot on a generally horizontal axis generally transverse to said beam of radiant energy and the center of gravity of said sensor means is generally vertically below said generally horizontal rotational axis.
 8. The machine of claim 1 wherein said generator means is in a given relationship with said reference means for movement therewith and said sensor means is in a given relationship with said working means for movement therewith.
 9. The machine of claim 1 wherein said working means comprises a digging wheel having a plurality of circumferentially spaced buckets thereon adapted to produce when rotated, a trench having a bottom surface in the terrain, and said reference means comprises a shoe adapted to be received in said trench behind said digging wheel and to bear on said bottom surface of said trench.
 10. The machine of claim 9 which also comprises an enclosure having a rigid hollow tube, a sensor housing connected to said tube adjacent one end thereof, and a generator housing connected to said tube adjacent the other end thereof with said sensor means mounted in said sensor housing and said generator means mounted in said generator housing such that said beam of radiant energy produced by said generator means passes through said hollow tube and impinges on said sensor means.
 11. The machine of claim 10 in which said first carrier means comprises means pivotally mounting said generator housing on said shoe and said second carrier means comprises generally vertically adjustable means mounting said enclosure adjacent said one end of said tube in an adjustable given relationship to the axis of rotation of said digging wheel.
 12. The machine of claim 1 wherein said working means comprises a rigid frame pivotally connected adjacent one end thereof to said vehicle and a digging wheel mounted on said frame for rotation thereon and having a plurality of circumferentially spaced buckets adapted to dig a trench having a bottom surface when said wheel is rotated in the terrain, and said reference means comprising a shoe positioned behind said digging wheel and fixed to said frame, said shoe being adapted to be received in the trench produced by said digging wheel and to bEar on the bottom surface of said trench with said shoe, frame and digging wheel being adapted to be pivoted in the trench about a point adjacent the trailing lower edge of said shoe as said one end of said frame is raised and lowered to control the grade of the bottom surface of the trench produced by the digging wheel, said generator means being carried by said first carrier means so that the point from which said beam of radiant energy eminates from said generator means lies generally vertically over said pivot point adjacent the lower trailing edge of said shoe.
 13. The machine of claim 1 which also comprises a detector apparatus enclosure having a rigid hollow tube, a sensor housing connected to said tube adjacent one end thereof, and a generator housing connected to said tube adjacent the other end thereof with said sensor means mounted in said sensor housing and said generator means mounted in said generator housing such that said beam of radiant energy produced by said generator means passes through said hollow tube and impinges on said sensor means.
 14. The machine of claim 13 which also comprises means mounting said sensor means in said sensor housing for adjustment of said sensor means generally transversely to said beam of radiant energy comprising a slide, an adjustment screw operably connected with said slide and being adapted to be manually rotated externally of said sensor housing to generally vertically reciprocate said slide within said sensor housing, and gimbal means carried by said slide with said sensor means mounted on said gimbal means.
 15. The machine of claim 1 wherein said sensor means comprises at least two photocells producing said electric signal indicative of vertical deviation of said working means from the desired grade, and said control means responsive to said electric signal comprises a hydraulic cylinder with a ram therein operably connected with said working means for vertically adjusting the position of said working means relative to said vehicle, an electro-hydraulic control valve adapted for selectively directing a hydraulic fluid under pressure into said cylinder to move said ram in said cylinder, and electric circuitry utilizing said electric signal of said sensor means to actuate and control said electro-hydraulic valve to direct hydraulic fluid under pressure into said cylinder to move said ram to adjust said working means to correct for said deviation of said working means from the desired grade as said working means is moved by said vehicle along the path of travel of the grade.
 16. A guidance system for controlling a working means carried by a machine for working a material to a desired grade as the machine travels along a given path by adjusting the working means relative to the machine, and said machine having a reference means movable with the machine and adapted to engage with the surface of the material previously worked to the desired grade by said working means, said guidance system comprising generator means for producing a beam of radiant energy generally in the direction of travel of the working means, stabilizing means for maintaining the beam of radiant energy produced by said generating means in a given stabilized attitude to project in said direction of travel of the working means, said stabilizing means being adapted for mounting in a given relationship with one of said working means and said reference means, sensor means extending generally transverse to and intersecting the beam of radiant energy produced by said generating means, said sensor means being spaced from said generating means and adapted for mounting in a given relationship with the other one of said working means and said reference means, said sensor means detecting relative motion between said sensor means and the point at which the beam of radiant energy impinges on said sensor means caused by relative movement between said reference means and said working means to produce an electric control signal indicative of deviation of said working meAns from the desired grade, whereby said electric control signal can be utilized to adjust said working means relative to the machine such that the material is worked to the desired grade as the working means is moved by the machine.
 17. The guidance system of claim 16 wherein said generator means comprises a laser light source.
 18. The guidance system of claim 17 wherein said stabilizing means comprises a gimbal having a first carrier adapted for rotation on an axis generally parallel to the beam of radiant energy produced by said laser light source and a second carrier mounted for rotation on said first carrier on an axis generally transverse to said axis of rotation of said first carrier, said laser light source being mounted on said second carrier for rotation therewith with the point from which the beam of radiant energy eminates generally coincident with the point of intersection of the axes of rotation of said first and second carriers, and a pendulum weight fixed to said second carrier such that the center of gravity of the combined laser light source, second carrier and pendulum weight is generally vertically below the point of intersection of the axis of said first and second carriers.
 19. The guidance system of claim 18 which also comprises a container receiving said pendulum weight therein and adapted to retain a liquid therein whereby the pivotal movement of said pendulum about the axes of said first and second carriers is dampened by the liquid.
 20. The guidance system of claim 18 which also comprises means connecting said pendulum weight with said second carrier such that the angular relationship between said second carrier and said pendulum weight can be adjusted.
 21. The guidance system of claim 17 wherein said sensor means comprises at least one photovoltaic cell.
 22. The guidance system of claim 16 which also comprises means mounting said sensor means so that said sensor means can rotate on an axis generally parallel to the beam of radiant energy produced by said generator means.
 23. The guidance system of claim 16 which also comprises means mounting said sensor means so that it can rotate on a first axis generally parallel to the beam of radiant energy produced by said generator means and can also rotate on a second axis generally transverse to the beam of radiant energy produced by said generator means and in which the center of gravity of said sensor means is generally vertically below the point of intersection of said first and second axes of rotation of said means for mounting said sensor means.
 24. The guidance system of claim 17 which also comprises an enclosure having a rigid hollow tube, a sensor housing connected to said tube adjacent one end thereof, and a generator housing connected to said tube adjacent the other end thereof, with said sensor means mounted in said sensor housing and said generator means mounted in said generator housing such that said beam of radiant energy produced by said generator means passes through said hollow tube and impinges on said sensor means.
 25. The guidance system of claim 16 wherein said sensor means comprises at least two photocells producing said electrical control signal indicative of vertical deviation of said working means from the desired grade and the guidance system also comprises electric circuitry utilizing said electric control signal of said sensor means to actuate and control an electro-hydraulic valve of the machine to direct hydraulic fluid under pressure into a fluid motor of the machine to adjust the working means to correct for said deviation of said working means from the desired grade as the machine travels along a given path such that the material is worked to the desired grade.
 26. A machine for working material to a desired grade along a given path in, on or over terrain comprising a vehicle for moving upon said grade, working means carried by said vehicle for working the material to the desired grade as the vehicle moves on the terrain aLong the given path, said working means being vertically adjustable in a given plane of motion relative to said vehicle, reference means movable with the machine and adapted to engage with the surface of the material worked on by said working means at a location wherein the surface of the material has been worked to substantially the desired grade by said working means, generator means for producing a beam of radiant energy in the general direction of said motion plane, sensor means spaced from said generator means and adapted to sense said beam of radiant energy, first carrier means carrying one of said generator means and said sensor means in a given relationship with said reference means for generally vertical movement therewith, second carrier means carrying the other of said generator means and said sensor means in a given relationship with said working means for generally vertical movement therewith, stabilizing means for maintaining the beam of radiant energy produced by said generator means in a given stabilized attitude to project in said motion plane, said sensor means being disposed generally transversely to and intersecting said beam of radiant energy, said sensor means detecting relative motion between said sensor means and the point at which said beam of radiant energy strikes said sensor means caused by relative generally vertical movement between said reference means and said working means and generating a signal indicative of vertical deviation of said working means from the desired grade, and control means responsive to said signal to adjust said working means generally vertically to correct for said deviation such that the material being worked remains at the desired grade as said working means is moved by said vehicle along said given path.
 27. The machine of claim 26 wherein said generator means comprises a laser light source.
 28. The machine of claim 27 wherein said stabilizing means comprises pivot means having an axis of rotation extending generally horizontally and transversely to said motion plane, said generator means being carried by said pivot means, and a pendulum weight rigidly connected with said generator means for pivotal movement therewith on said axis with the combined center of gravity of said generator means and said pendulum weight being generally vertically below said axis. 